Modern medium-frequency melting systems are characterized by high levels of energy efficiency. In aluminium melting, for instance, around 65 % of the power input are converted into useful heat. This is a good rate but one that nevertheless leaves scope for further savings.

Most of the energy loss is caused by the induction coil. In aluminium applications, this amounts to approx. 25 - 30 %.

As reported in a previous issue (refer to OTTO JUNKER News No. 15), the use of a special coil design providing an enlarged current-carrying surface area has made it possible to reduce these losses. Thus, energy savings of around 7 % for aluminium and 9 % for copper can be achieved. By now, more than 70 energysaving coils are operating successfully in furnaces for all common casting metals.

It should be noted that this new coil can also be retrofitted into existing coreless furnaces. It thus suggests itself for equipment upgrades as well, as in the present project.

At the Děčín plant, a total of three medium- frequency coreless induction furnaces supplied by OTTO JUNKER over of the past 20 years are successfully in use. Varying in size, these units have power ratings of 2,600 kW and 4,000 kW, respectively. They handle a broad range of different charge materials, from remelting ingots, chips and lumps to residues from the fabrication of semifinished products (billets, pipes, extrusions and rods).

Under a public contract, OTTO JUNKER will now convert these plants to the new energy-saving coil technology in conjunction with the installation of OCP optical coil protection systems. The aim of the revamp is to achieve a 7 % energy saving based on a consumption of 530 or 520 kWh/t, respectively. The positive results attained with the energy-saving coil in OTTO JUNKER furnaces at Constellium's Issoire plant leave no doubt that this target will be met.

For the disassembly and installation of the new coils, a period of 11 days has been scheduled. This will be split into two stages, i.e., the first two furnaces are to be converted in late July while the third will be rebuilt in early December.